I like Susan Kare's work. But I think the under-rated talent is Keith Ohlfs, who was behind NeXT's beautiful and functional UI and icons, and who later went on

I like Susan Kare's work. But I think the under-rated talent is Keith Ohlfs, who was behind NeXT's beautiful and functional UI and icons, and who later went on to do a lot of other interesting stuff, including the UI for WebTV as well.